A. Field of the Invention
The present invention relates to a paper feeding device that uses air suction for manipulation of paper in an image forming apparatus, such as electrostatographic copying machines, facsimiles, printers and the like.
B. Description of Related Art
There are paper feeding device which uses air suction in which airflow is applied to stacked papers to lift and separate the papers from one another, and an uppermost paper of the stacked papers drawn away and transferred by vacuum from a vacuum device.
Such devices are characterized in that a groove for introducing airflow is provided in an end portion opposite to a nozzle disposed on a bottom plate of a tray on which papers are stacked. Even for a small amount of remaining papers, airflow from the nozzle is introduced into the groove to lift the end of papers, so as to ensure the vacuum and transfer of an uppermost paper.
In the device described above, however, the groove is provided only in the end portion of the bottom plate of the tray, and the area of contact between a final paper and the bottom plate is large. Therefore, when strong static forces due to, for instance, static electricity are present, the final paper may resist lifting even if air flow is present into the groove.
Further, regardless of the type of paper, or thickness of paper in the device, the air flow through the groove is generally constant. Since thin papers are light, they may be lifted too forcefully and since thick papers are heavy, they might not be lifted at all. Thus, it is difficult to determine an appropriate amount of vacuum pressure to create an appropriate flow of air to move paper.
There is also a paper feeding device which includes a pressure foot member structurally free to move up and down between a paper transferring belt and an uppermost paper in a stack of papers. The pressure foot member may selectively supply airflow from a front portion thereof to expand the air between an uppermost paper and an underlying paper, so as to produce reliable separation of the two papers.
When a pressure foot member is provided, it is necessary to provide a plate for contacting the rear end of paper, where the plate is adjustable back and forth. Space is limited in such devices and thus reducing the degrees of freedom of design. Further, the overall number of parts increases, resulting in higher cost.